1. Field of the Invention
The present invention relates to a winding core and more particularly a winding core for winding up an ink ribbon accommodated rotatably within a ribbon cassette and having been used in printing.
2. Description of the Prior Art
A thermal transfer printer has heretofore been used in which a predetermined paper is conveyed to between a platen and a thermal head as a recording means while being held between a conveying roller and a pressure roller which is brought into pressure contact with the conveying roller, then the thermal head is moved along the platen while it is kept in pressure contact with the platen through the paper, and heat generating elements of the thermal head are allowed to generate heat selectively in accordance with a recording signal while the ink ribbon is wound up to melt-transfer the ink of the ink ribbon onto the paper, thereby performing a desired recording on the paper.
FIG. 10 is a perspective view showing a schematic construction of a carriage portion 23 of a conventional thermal transfer printer 21. A platen 22 in the shape of a flat plate is disposed near the central part of a frame (not shown) so that its printing surface is substantially perpendicular to the frame, a guide shaft 27 is disposed at a lower position in front of and in parallel with the platen 22, and a carriage 23 is mounted slidably on the guide shaft 27. A driving belt 28 entrained on a pair of pulleys (not shown) is driven by means of a stepping motor (not shown), whereby the carriage 23 is reciprocated on the guide shaft 27.
A thermal head 24 is mounted on a front end portion of the carriage 23 in an opposed relation to the platen 22. The thermal head can move into contact with and away from the platen 22 through an appropriate mechanism. A ribbon cassette 26 (see FIG. 13 ) is loaded onto the upper surface of the carriage 23. The ribbon cassette 26 contains an ink ribbon 25 and conducts the ink ribbon to between the thermal head 24 and the platen 22.
On the carriage 23 are disposed a winding mechanism 29 and a supply mechanism as constituents of an ink ribbon traveling mechanism to move the ink ribbon 25 in the direction of arrow A in the figure.
The ink ribbon traveling mechanism will be further described below.
As shown in FIGS. 11 and 12, the winding mechanism 29 has a winding shaft 30. The lower end portion of the winding shaft 30 is integrally formed with a support flange 32 projecting outward, and a winding gear 31 is loosely fitted on the said lower end portion in a rotatable manner independently of the winding shaft 30. Between the underside of the winding gear 31 and the support flange 32 of the winding shaft 30 is interposed a felt 33 as a slip mechanism, while to the upper end portion of the winding shaft 30 is fixed a winding bobbin 35 which is exposed to the upper surface of the carriage 23 and engaged with a winding hole 34 formed in the ribbon cassette 26. On an outer peripheral surface 36 of the winding bobbin 35 are formed three engaging projections 37 at circumferentially trisected positions, and an annular retaining groove 38 is formed in the lower surface of the winding bobbin 35. On the outer periphery side of the winding shaft 30 is disposed a biasing spring 39 whose upper end portion is retained by the retaining groove of the winding bobbin 35 and whose lower end portion is abutted against the upper surface of the winding gear 31. With the biasing force of the biasing spring 39 the winding gear 31 is brought into pressure contact with the support flange 32 of the winding shaft 30 through the felt 33.
A driving gear 40 fixed to a rotating shaft 48 of a winding motor 47 for the ink ribbon 25 meshes with the winding gear 31. The driving gear 40 is rotated by operation of the ink ribbon winding motor 47 to thereby rotate the winding gear 31. This rotative driving force is transmitted to the winding shaft 30 by virtue of a frictional force of the felt 33 which is created by the biasing force of the spring 39 which is for urging the winding gear 31.
As to the foregoing ink ribbon supply mechanism, an explanation thereof is here omitted.
On the other hand, as shown in FIG. 13, the ribbon cassette 26 loaded onto the upper surface of the carriage 23 is constituted by a case body 41 which is generally rectangular in plan and which comprises a pair of upper case 41A and lower case 41B. In the interior of the case body 41 are disposed a pair of cores 42, 42 supported rotatably, a pair of pinch rollers 43,43 also supported rotatably, and a plurality of guide rollers (not shown) supported rotatably and facing the ribbon traveling path.
The paired cores 42, 42 are each formed in a generally cylindrical shape, and the ink ribbon 25, which has characteristics of heat sublimation or heat melting, is wound from both ends thereof on the outer peripheral surfaces of the cores 42, 42. When the paired cores 42, 42 are loaded onto the carriage 23 of a printer for which the ribbon cassette 26 is used, the core 42 located on the left-hand side in FIG. 13 is used as a winding core 42A for winding a portion of the ink ribbon 25 which portion has been used in recording, while the core 42 located on the right-hand side in the same figure is used as a supply core 42B for supply of the ink ribbon 26 in recording.
In an inner peripheral surface 44 of each core 42 are formed a plurality of engaging grooves 45, 45 in a spline shape spacedly in the circumferential direction. Inside of the inner peripheral surface 44 of the left-hand winding core 42A in FIG. 13 is used as a winding hole 46A for engagement therein of a winding bobbin 35A formed on the carriage 23 of the printer, while inside of the inner peripheral surface of the right-hand supply core 42B in FIG. 13 is used as a supply hole 46B for engagement therein of a delivery bobbin 35B which constitutes the foregoing supply mechanism.
In loading the ribbon cassette 26 onto the carriage 23, there sometimes occurs the case where the ink ribbon 25 accommodated in the ribbon cassette is slightly slack between the paired cores 42, 42. In this case it has so far been required for the user to manually wind up the slack portion of the ink ribbon 25.
Moreover, in the inner peripheral surface 44 of each conventional core 42 are merely formed a plurality of engaging grooves 45, 45 in a spline shape spacedly in the circumferential direction, so after loading of the ribbon cassette onto the carriage 23, dust gets into the engaging grooves 45, 45 from the upper openings, thus resulting in that rotation is not stable during winding of the ink ribbon 25 and the traveling of the ink ribbon becomes unstable, leading to deterioration of the print quality.
Further, since the ribbon cassette 26 can be loaded onto the carriage 23 irrespective of the width of the ink ribbon 25 used, there has been the problem that an ink ribbon 25 of a narrow printing width is accommodated in the ribbon cassette 26.
The above problems are not limited to between the winding bobbin 35 on the carriage 23 of the foregoing thermal transfer printer and the winding core 42A in the ribbon cassette 26 loaded on the carriage, but may occur also between a winding core in a cassette which receives therein a label printing tape or the like in a wound-up state and a winding bobbin formed on a body such as a label printer onto which the cassette is to be loaded.